【1.Theforestsofthetropicsproduceamagnificentgrowthoftrees,butcommerciallumberingisinhibitedbyproblemsthatincreasethecostofremoval.Theproliferationofspeciesthatiscommontoalltropicalforestscreatesdifficultiesbecausema】

　　1.Theforestsofthetropicsproduceamagnificentgrowthoftrees,butcommerciallumberingisinhibitedbyproblemsthatincreasethecostofremoval.Theproliferationofspeciesthatiscommontoalltropicalforestscreatesdifficultiesbecausemanyspeciesareworthless.Thelumbermancombstheforest,therefore,removingthevaluabletreesthatareconvenienttowaterways,andfloatingthemdownstreamtoasawmill.Unfortunately,tropicalhardwoodstendtogrowslowly;anareaonceclearedneedssubstantialtimetorecover,forcingthesawmillstobecomemobile.Distancetomarkettendstobeconsiderable,raisingcostsoftransport.Becauseofthesedifficulties,onlythemostvaluablewoodscanabsorbthehighcostsassociatedwithproduction.Othertreesareleftuntouched.

　　1).Accordingtothepassage,oneoftheproblemsofcommerciallumberingis____.

　　A.selectingvaluabletreesisdifficult

　　B.thereislittlevarietyinthetypesoftreesintheforests

　　C.manyofthetreesareuselessfortimber

　　D.veryfewhardwoodsgrowintheforests

　　2).Thelumbermensearchtheforestsforvaluabletreesandchoosetheonesthat____.

　　A.aretropicalspecies

　　B.areeasytocutdown

　　C.areneartorivers

　　D.matureveryslowly

　　3).Accordingtothepassage,thesawmillshavetobemobilebecausetheyare____.

　　A.floateduptherivers

　　B.transportednearthemarkets

　　C.movedawayfromclearedareas

　　D.usedtotransportwood

　　4).Accordingtothepassage,relativelyfewtreesareremovedfromtheforestsbecause____.

　　A.onlythemostvaluablejustifythecost

　　B.theproliferationofspeciescannotabsorbthehighcosts

　　C.thetropicalhardwoodsareexpensivetoproduce

　　D.itistooexpensivetotransportthehardwoods

　　5).Whatcanbeassumedfromtheinformationgiveninthepassage?

　　A.notenoughspeciesgrowneartherivers.

　　B.usefulspeciesdonotreproducequickly.

　　C.toomanyspeciesgrowintheforests.

　　D.tropicalforestsproducetoomanytrees.